effective SELECT from child tables

Let table A be inherited by A1, A2, A3.

How to select from A records where actual relations are A1, A2 ?

I found a way somewhere, it sounds like SELECT  … WHERE tableoid IN (a1.oid, a2.oid),

but tableoid checks actually do seq scan.

Like: SELECT * FROM sometable WHERE tableoid =anything will do seq. scan on sometable..

So such way seems very ineffective: it seq scans and filters records..

Maybe new constraint_exclusion staff could help to exclude non-matching tables from inheritance query ?